French doors and bi folds need hinges that are strong enough to withstand the weight of the doors. Sliding doors (including bi folds) can be supported from the top or rest on the floor. Top hung systems tend to be easier to slide and will facilitate low thresholds. Thresholds can be raised or virtually flush, if the floor area is suitable. Raised is usually cheaper and may be more suitable to certain environments; other factors to consider are access by wheelchair users, young children and elderly, infirm or partially sighted people who may be liable to trip. Consideration should be given to how secure patio doors are. Not only the quality of the frames and glass but whether the doors can be unlocked from the outside. French doors are often purchased "off the shelf" and afford access from both sides whereas bifolding doors are often made to measure and can be supplied with locks on the inside only. Multiple door systems may have key-locks for each of the pairs of doors for extra security.

Access & Opening Widths

To recap, French doors come in pairs and therefore the maximum access width is in the region of 2 metres. Sliding doors comprise two, three or four sashes within a frame, the larger systems opening to provide maximum access width of approximately 3 metres. Bi-folding and slide-and-pivot door systems are fully retractable, maximising the potential access width. The width-span of bifolds is governed by the stress of the hinged doors therefore a link of six doors is considered the maximum although, in theory, two of these could be installed to form a centrally opening retractable glass wall of twelve doors spanning 12m, provided the overbeam can be trusted (reputable companies will probably advise against this). Without hinges and cumbersome frames, slide-and-pivot doors are lighter and operate independently, therefore their installable width span is restricted only by the length of the over-beam to which the upper guide needs to be attached. The upper and lower guides must be consistently equidistant along the full width of the aperture for the doors to slide. This system has been tested to approximately 8 metres.

Delivery & Installation

As previously stated, French doors can usually be purchased 'off the shelf' to standard sizes, as can smaller widths of sliding doors and pvc or timber bi folding door systems. If purchasing a system that is made to order, it is advisable to ensure that it is manufactured in the UK. Main benefits include adherence to British standards and delivery timescales (not only for the initial import but for subsequent parts or problem solving). When comparing prices, include: cost of buying the door system, delivery service, installation labour (if d-i-y, cost of appropriate tools and materials), making good and clearing the site. Price is not everything, though. Consider the time it takes for the installation to be completed - typically, an experienced team from the supplier will complete the job in a day so that home-owners can enjoy using their new patio doors as soon as possible.

All patio doors are required to have double glazing, although glass room dividers and glass doors to non residential properties can be single glazed tempered "unbreakable" glass.

A visible "kitemark" on the glass is the consumers' assurance that the double-glazed unit has been manufactured to British standards. The BSI has numerous standards, including: U-value verification, Window Energy Rating and Window Installation. The lower the U-value, the better the thermal performance and most local authorities will require this to be 1.8 or better to meet building regulations.

Some manufactures offer optional extras, such as tinted glass, anti-sun, laminated, obscured glass and Argon-filled double-glazing. It is also possible to match existing period features by specifying Georgian bar or leaded-light in rectangular or diamond style. An innovative option is switchable privacy glass which enables molecules inside the double-glazing to become transparent or opaque at the press of a button; this is expensive, though, typically doubling the original price of good quality patio doors.

An alternative solution is to order patio doors with integral horizontal blinds, factory sealed inside the double-glazing cavity. Proven to be reliable, the blinds can be operated via a magnet system (there is an alternative electronic option) that enables the slats to be easily angled to control the amount of light filtering through and can also raise and lower the blinds for maximum light or shade. A major advantage of opting for internally sealed blinds rather than separate blinds is that they are totally maintenance-free - no arduous dusting or cleaning - and because the blinds are encapsulated inside the glazed panels, they are exceptionally difficult to break.

Patio doors comprise an outer frame plus individual door frames. These can be made from wood (soft- and/or hard-wood), metal or alloys (usually aluminium), pvc (polyvinyl chloride, a thermo-plastic polymer - the 'u' stands for unplasticised) or a composite material, which may comprise any of the foregoing materials plus grp (glass reinforced polymer). There is also a style known as frameless, where the vertical sides of each door have no frames.

Generally, timber frames are considered more traditional and can look beautiful! Hard wood such as oak is, as the name suggests, far more hard-wearing than a soft wood such as pine. Weather, especially strong sun, can take its toll on timber frames which could need to be varnished or painted annually. Wooden frames can swell and shrink with humidity, therefore opening and closing doors can require force and gaps can allow draughts in colder temperatures.

Metal frames, usually aluminium, provide strength in compact form. As notoriously good conductors (which is a bad attribute for insulation), frames made from aluminium are thermally-broken, which is a good attribute. It means that the metals on the inside and outside of the door frames are not joined, preventing the temperatures from being transferred between them. A bare metal frame would look completely unattractive so it is powder-coated in a choice of over 100 standard colours, including a white that resembles pvc.

As with timber, the quality of pvc frames available can vary - and generally, you get what you pay for. The better ones will usually be reinforced with metal, internally, for greater strength but the cheaper options can be a nightmare to live with - sticking, twisting, splitting, discolouring, warping - often within a very short time. Most usually supplied as white, some manufacturers offer limited colour options or wood effect finishes.

Whilst frameless doors have no side frames, the top and bottom of each door requires a mechanism, typically presented in aluminium, to allow it to slide within the top and bottom guides. Frameless glass doors have the best sight lines.

Sight lines is the term used to describe the interruptions in the view through the doors; in other words, the width of the vertical opaque areas between the glass when the doors are closed. On hinged doors, such as French doors and bi folding doors, timber and pvc frames generally have broad sight lines because, unlike aluminium, narrower frames would not be strong enough to be fit for purpose. As a guide to the width of two frames together, cheaper pvc door frames can exceed 200mm, aluminium frames are typically between 135mm and 160mm and frameless patio doors sight lines are under 40mm. Depending on the width of each door and number of doors to be installed, the difference in glass to frame ratio could be significant.

Door profiles - the width of the visible door edges when open - may be a consideration. Additionally, some door profiles are ugly, showing mullions or working parts that would be better hidden from view.

Thursday, 12 January 2012

Traditional or modern? Classic or contemporary? Varying tastes and different architectures throughout the years, as well as innovations and enhanced lifestyles, have given rise to the wide choice in patio door variations currently available in Britain. This article aims to describe the types of patio doors - their styles and functionality, similarities and differences, together with some of their main advantages and popular options - in order to provide readers with an informative guide.

The latest patio doors innovation is slide-and-pivot doors. Developed and launched since 2007/8, slide-and-pivot doors incorporate the major benefits of bifolding doors and sliding patio doors. Comprising a number of individual glazed panels that fit snugly together when closed, there is a 'master' door that can be opened with a standard (pivot) action, enabling the other doors to be moved, individually, along the top and bottom guides; as each door is moved to the end of the guides, it can also pivot open to increase the access width between the divided areas ( to a suggested maximum of approximately 8 metres).

Because slide-and-pivot doors have no hinges, there is no requirement for a sturdy side frame; its only purpose is to cover the gasket that seals the double glazed unit. This means that the views afforded through the expanse of patio doors have minimal interruptions. At the time of writing, there are two versions of frame-less glass doors available in the UK, both using the slide-and-pivot technique: one manufacturer supplies their frameless glass doors with kite-marked double glazed units which have a visible seal, the other uses an almost transparent method of sealing their double glazing. Contemporary by design, the absence of visible characteristics makes frameless glass doors a viable option for period properties.

Bi Folding doors were launched around the turn of the century; they can be installed in place of French doors, where both doors are hinged to fold as they open together to one side. Bi folding doors can also span an opening to around 7 metres wide, depending on the frame chosen. A 'master' door can be placed amongst the doors, at the ends or in the middle, wherever the opening is required; this door is a standard (pivot) opening door which enables the other doors to be pushed to the side or sides of the aperture, resulting in a sliding-folding action, concertina-style, to maximise the width of the opening between home and garden or conservatory.

Originally, patio doors were all of the French Door variety; that is, a pair of doors that are hinged at the sides and open from the middle, each door pivoting in- or out-wards. French doors are still popular, especially with builders of new homes, as they are comparatively cheap and easy to accommodate in place of windows and offer an alternative evacuation route for families, especially for elderly or disabled people, to meet improved fire safety requirements.

Arguably, French doors could be considered as retractable as each door can be pulled back. The advantage of retractable doors is that maximum access is possible between the two sides of the aperture whereas sliding panel doors generally overlap unless built to retract into a recess.

In the mid-20th century, sliding doors became very popular - two or three panels of glass that slide along grooves in the floor. To distinguish them from traditional French doors, they were marketed with the thoroughly modern name of Patio Doors and this is often the image people have today when that term is used. Easily installed in place of a window, the immediate advantages were additional natural light and access to the garden. They also became a popular option to use where a pivot door opening space was limited or where the aperture was wider than a pair of French doors. Older installations were typically single-glazed, prone to warping and usually became difficult to slide open and closed. Still available today but in a developed form with double glazing and rollers for easier sliding, the popularity of sliding doors during this century has declined as bifolding doors gained market share.